A lot of genes involve in C.elegans cell fate determination and linage development. Par genes activities are responsible for establishing anterior and posterior axis. Loss of par function results in loss of AP asymmetries during the first two embryonic cell divisions and a failure to restrict developmental regulators to specific embryonic cells and abnormal cell fate patterning.
pal-1 is an important gene which is required to determine the cell fate of posterior blastomeres in C.elegans early embryo. It's a Caudal-like homeodomain protein and specifies the production of body muscle and epidermis by the P2 daugher cells of P1 (Hunter and Keynyon,1996). A lot of genes regulate the expression of PAL-1. Except for
mex-3 ,
par-1、
par-3、
par-4 gene also affect the expression of PAL-1 in early embryo as well as the
mex-5,
mex-6 and
spn-4(Nancy N Huang et al 2002). These genes affect the expression and distribution of PAL-1 through regulating the MEX-3 distribution. In order to understand which lever these genes regulate the pattern of PAL-1 expression, we have analyzed the distribution of
pal-1 mRNA in C.elegans early embryo of wild type,
par-1、
par-2、
par-3、
par-4、
spn-4 mutant and
mex-5/mex-6 mutant via in situ hybridization. The observed
pal-1 mRNA expression pattern are summarized below:
pal-1 mRNA in wild type N2 embryo shows asymmetric localization in one cell, two cell and 4-cell embryos. At 4-cell embryo, posterior 2 cells present high level than anterior cells. In
par-1(
b274)、
par-3(
e2074)、
par-4(
it47) mutant embryos, pal-1mRNA lost asymmetric localization and present everywhere. Loss function of
par-2 (
it5) does not affect the distribution of pal-1mRNA. At 4-cell embryos, posterior 2 cells present high level than anterior cells, same pattern as wild type embryos.
spn-4(
or80) and
mex-5(
zu199)
mex-6 (
pk440) also affect pal-1mRNA asymmetric distribution. Loss function of
spn-4 or
mex-5 mex-6, pal-1mRNA lost asymmetric localization and present everywhere. In
spn-4 mutant embryo, 2 posterior cells darker staining than 2 anterior cells at 4-cell embryos. In
par-1、
par-4 mutant, pal-1mRNA present everywhere but no PAL-1 detected in any cells of 4-cell embryos(Bruce Bowerman et al 1997). It implies that
pal-1 mRNA distribution is relate to activity of the polarity gene in C.elegans early embryo and the translational regulation of pal-1mRNA may be the reason of spatially and temporally asymmetric location of PAL-1 protein.